(1) Field of the Invention:
This invention relates to surgical fibers, such as sutures, obtained from polyglycolic acid, poly(l-lactic acid) or a glycolic acid-l-lactic acid copolymer, specifically, to blue-colored bioabsorbable surgical fibers obtained from the above polymer and to a production process thereof.
(2) Description of the Invention:
Polyglycolic acid, poly(l-lactic acid) and their copolymers are solid and have high bioabsorbability and hydrolyzability. Those having high polymerization degrees are spun or braided or processed into non-woven fabric and are hence used as surgical materials such as surgical sutures and gauze.
These bioabsorbable high-molecular materials have grayish yellow colors or substantially translucent gray colors, for example, when they are spun for use as sutures. When they are used as sutures in surgery, they are therefore stained in a red color with blood so that the stitched parts are hardly distinguishable and their distinction often presents difficulties during the surgery.
In order to solve such a problem, there have been known those colored with desired various pigments so as to permit their distinction at first glance even after stained with blood, in the case of sutures made of materials other than bioabsorbable high-molecular materials, for example, nylons, polyesters and the like. Such pigment-dependent coloring did not cause any problem in the case of sutures made of materials to be taken out after completion of suture, like aforementioned nylons and polyesters.
However, sutures made of bioabsorbable high-molecular materials are not taken out owing to their advantage even after completion of suture of surgical sites. A coloring agent which is employed to color sutures made of such a bioabsorbable high-molecular material is supposed to be non-toxic to human bodies and at the same time to be promptly absorbed and excreted. As a corollary, a limitation is naturally imposed on usable coloring agents.
Under the above-described circumstances, United States Food and Drug Administration has established a guideline as to the coloring of surgical sutures made of bioabsorbable high-molecular materials that they may be colored with coloring agents authorized as non-toxic by the Administration. Various specifications and standards have also been established with respect to tar dyes for foods, drugs and cosmetics in Japan. Tar dyes usable in drugs and quasi-drugs for external use are listed up ("Manual of Dyes", pp 222-223).
Among such dyes, certain oil-soluble dyes have already been known to be useful for coloring bioabsorbable sutures and the like. In U.S. Pat. No. 4,008,303, 1,4-bis(p-toluidino)anthraquinone (C.I. Solvent Green 3) is used as a coloring agent suitable for use in coloring polyglycolic acid. U.S. Pat. No. 3,839,297 discloses the use of 1-hydroxy-4-p-toluidinoanthraquinone (C.I. Solvent Violet 13) as a coloring agent for sutures made of glycolic acid-lactic acid copolymers.
These coloring agents are however oil-soluble ones which are employed usually as colorants for resins. When employed directly in human bodies, they are not absolutely considered to be non-toxic. Further, the coloring agent disclosed in U.S. Pat. No. 4,008,303 is a green one. Sutures colored by this coloring agent are therefore turned into a black color upon adhesion of blood, thereby making it difficult to distinguish them. On the other hand, the coloring agent described in U.S. Pat. No. 3,839,297 is a purple dye. Vividly-colored bioabsorbable high-molecular materials cannot be obtained unless their coloring with the coloring agent is effected by adding the coloring agent in the course of the polymerization of the materials. It has however been found that the coloring agent is caused to evaporate to a considerable extent during the polymerization and its loss is unignorably substantial.
As has been described above, none of such conventionally-known coloring agents are satisfactory as coloring agents for bioabsorbable high-molecular materials.